Method and apparatus for transmitting data

ABSTRACT

In a method for transmitting data of various traffic types an xDSL modem is utilized. Detectors are used to detect the traffic types of the data which are to be transmitted and the detected traffic types are taken as a basis for dynamically adjusting a data transmission rate for the xDSL modem.

RELATED APPLICATIONS

This Application is a Continuation Application of U.S. patentapplication Ser. No. 11/641,316 filed on Dec. 19, 2006 now U.S. Pat. No.8,005,977. U.S. patent application Ser. No. 11/641,316 claims prioritybenefit of Germany Patent Application 102005060968.6, which was filed onDec. 20, 2005. The entire contents of U.S. and German filed Applicationsare incorporated herein by reference.

BACKGROUND OF THE INVENTION

The invention relates to a method and an apparatus for transmittingdata.

xDSL methods (DSL: Digital Subscriber Line) are transmission-relatedmethods for the digital use of twisted pairs of telephone wires in asubscriber access network. The subscriber access network is a network towhich a multiplicity of subscribers are connected by means of arespective telephone line. In the case of xDSL, a distinction is drawnbetween symmetrical and asymmetrical xDSL variants. In the case of theasymmetrical ADSL, the data transmission rates downstream, i.e. towardsthe subscriber, at up to 8 MB/sec., are much higher than the datatransmission rate of 1 MB/sec. which can be achieved upstream. In mosthouseholds, Internet access via the existing copper pairs is used. Thecontinually rising need for bandwidth also means that what is known asVDSL (Very High Speed Digital Subscriber Line, ITU-T Standard G.993.1G.993.2) technology is also being introduced in steps, this technologyallowing data rates of up to 100 MB/sec. to be achieved in bothdirections on short lines.

The attainable data rates are dependent on the signal-to-noise ratio SNRon the respective telephone line. As the line length increases and asthe crosstalk from other telephone line pairs increases, the data ratewhich can actually be attained decreases. The current practice of anetwork operator for configuration during operation of a DSL line is forthe customer or subscriber to have a fixed data rate agreed for hisInternet access which is significantly below the physically achievabledata transmission rate. This agreed low fixed data transmission rate isalso still achieved on longer telephone lines, even if disturbingadjacent DSL signals occur. Alternatively, network operators guarantee aminimum data transmission rate and then set a possibly higher possibledata transmission rate on the basis of the actual line conditions whenclearing the DSL line (Best Effort).

It is becoming increasingly important for DSL network operators toprovide voice services (Voice Over IP) and films (Video On Demand) usingDSL in future. This significantly increases the need for bandwidth.Transmitting voice data using Voice Over IP and transmitting image datamake special demands on the DSL connection. Voice data have a low datatransmission rate of below 100 KB/sec. but are particularly sensitive toa long signal propagation time or signal propagation time fluctuations,since these mean that signal components reflected at the far end of thesubscriber line are perceived by the subscribers as an irritating echo.Merely a total propagation time of above 30 msec. reduces the subjectivequality of the telephone call. A DSL voice link should therefore ideallynot contribute more than 5 msec. to the total propagation time.

Video or image data use image compression techniques which result in adata transmission rate of between 2 MB/sec. and 20 MB/sec. The real-timecharacter of the video data stream does not allow the repeatedtransmission of data packets which have been lost, as is customary withthe TCP protocol, for example (TCP Over IP). If RTP data packets (RTP:Real Time Protocol) are lost, this results in brief picture noise.Retransmission of lost data packets for image data transmission ispossible only if a sufficiently large buffer store is provided at thereceiver end which can compensate for the time loss in the event of afresh packet request. However, a large buffer store has the drawbackthat a change of channel or a change of program results in long idletimes when emptying or refilling the buffer store, or else a very largebandwidth needs to be provided on the DSL line which is significantlyhigher than the ascertained data rate required for transmitting a singlevideo data stream.

Impulse noise occurring on a DSL connection can result in a brief lossof data. For pure Internet data, such as web data, or e-mail data, suchdata losses caused by impulse noise are totally unnoticeable to thesubscriber thanks to TCP retransmission, i.e. fresh transmission ofdata. Even when voice data are being transmitted, impulse noise merelycauses an audible noise, but this is barely perceived by thesubscribers.

Both ADSL and VDSL are equipped with an error correction mechanism wherethe transmitter adds redundant data to the data stream which allow aparticular volume of noisy data to be reconstructed at the receptionend. This error correction allows bit errors caused by impulse noise tobe corrected. In this case, bit errors when pulsed noise signals occurare avoided by distributing the bit information over the DSL connectionin the course of time, or “interleaving” it. Without interleaving, apulsed noise signal can disturb both the actual useful data and theredundantly added error correction data. However, interleaving the dataresults in an additional signal propagation time which is typicallybetween 80 and 20 msec. in order to provide adequate protection againstpulsed noise signals. Pulsed noise signals normally have a duration ofless than 0.5 msec. During the occurrence of a pulsed noise signal, thedata contained in the data stream are completely destroyed. The longersignal propagation times caused by interleaving can be accepted withoutany drawbacks for video or image data. By contrast, longer signalpropagation times caused by interleaving have a disruptive effect whentransmitting voice data and possibly also when transmitting Internettraffic where timing is critical, for example “online gambling”.

Generally, the various traffic types of data, particularly Internetdata, voice data and video data, place partly conflicting demands on theconfiguration of the DSL connection and hence of the xDSL modem.

BRIEF SUMMARY OF THE INVENTION

The invention provides a method for transmitting data of various traffictypes using an xDSL modem, wherein detectors are used to detect thetraffic types of the data which are to be transmitted and the detectedtraffic types are taken as a basis for dynamically adjusting a datatransmission rate for the xDSL modem, with framing and interleavingpreferably also being adjusted.

In one embodiment of the inventive method for transmitting data ofvarious traffic types using an xDSL modem, the following steps may becarried out:

a data transmission rate for the xDSL modem is initialized to aprescribed minimum transmission rate for transmitting data of a datatraffic type;

it is detected whether data of at least one other traffic type need tobe transmitted by the xDSL modem, and

the data transmission rate is set to a prescribed minimum total datarate for transmitting data of the data traffic type and data of thefurther detected traffic types; the set data transmission rate isincreased in steps at prescribed intervals of time; andthe set data transmission rate is reduced to the minimum total data rateif a deterioration in connection quality is detected.

In one embodiment of the inventive method, the various traffic types maycomprise a data traffic type for transmitting information data,particularly Internet data, a voice traffic type for transmitting voicedata and a video traffic type for transmitting image data.

In this case, the data transmission rate of the xDSL modem may be set bya flow controller using SRA (Seamless Rate Adaptation).

In one embodiment of the inventive method, a voice data detectorconnected to the flow controller may be used to detect whether the datapackets coming from a data source contain voice data.

In one embodiment of the inventive method, a video data detectorconnected to the flow controller may be used to detect whether the datapackets coming from a data source contain image data.

In one embodiment of the inventive method, the data to be transmittedmay be distributed over various transmitted-signal paths for the xDSLmodem by a time-division multiplexer.

In one embodiment of the inventive method, the distributed data in eachtransmitted-signal path may be grouped by a framer to form an xDSL datatransmission frame.

In one embodiment of the inventive method, the data to be transmitted inthe xDSL data frame in each transmitted-signal path of the xDSL modemmay be encoded by an associated error protection unit in order toprotect against transmission noise.

In one embodiment of the inventive method, a test digit for each xDSLdata transmission frame which is to be transmitted may be generated bymeans of a CRC (Cyclic Redundancy Check) encoder.

In one embodiment of the inventive method, the data to be transmitted,including the generated test digit, may be scrambled by a scrambler inthe error protection unit.

In one embodiment of the inventive method, the scrambled data may beencoded by a Reed-Solomon encoder in the error protection unit.

In one embodiment of the inventive method, the data encoded by the errorprotection unit may be interleaved by a downstream interleaver containedin the transmitted-signal path which has an adjustable interleave depth.

In one embodiment of the inventive method, the signal propagation timeof the various transmitted-signal paths of the xDSL modem may be set byaltering the interleave depth of the associated interleaver for thevarious traffic types.

In one embodiment of the inventive method, the occurrence of impulsenoise may prompt the signal propagation time to be set to maximum if avideo data detector detects that the data packets coming from the datasource contain image data.

The invention also provides an apparatus for transmitting data ofvarious traffic types using an xDSL modem, wherein detectors can be usedto detect the traffic types of the data which are to be transmitted, andthe detected traffic types can be taken as a basis for dynamicallyadjusting a data transmission rate for the xDSL modem.

DETAILED DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

To explain features which are fundamental to the invention, the textbelow describes preferred embodiments of the inventive method and of theinventive flow controller for transmitting data of various traffic typesusing an xDSL modem with reference to the appended figures, in which:

FIG. 1 is a circuit arrangement with an xDSL modem and an inventive flowcontroller.

FIG. 2 is a block diagram of an exemplary embodiment of the xDSL modemactuated by the inventive flow controller.

FIG. 3 is a flowchart of exemplary embodiment of the inventive methodfor transmitting data of various traffic types.

FIG. 4 is a flowchart of a subroutine within the inventive method shownin FIG. 3.

FIG. 5 is a flowchart of a further subroutine within the inventivemethod shown in FIG. 3.

FIG. 6 is a flowchart of a further subroutine within the inventivemethod shown in FIG. 3.

FIG. 7 is a flowchart of a further subroutine within the inventivemethod shown in FIG. 3.

BRIEF DESCRIPTION OF THE INVENTION

FIG. 1 shows a preferred embodiment of the inventive flow controller 1for carrying out the inventive method, shown in FIG. 3, for transmittingdata of various traffic types using an xDSL modem 2. The preferredembodiment of the xDSL modem used in this case is shown in FIG. 2. ThexDSL modem 2 has a subscriber access point 4 connected to it by means ofa subscriber line 3. The xDSL modem 2 sends and receives modulated datavia the subscriber line 3.

The xDSL modem shown in FIG. 2 is a dual latency xDSL modem having twotransmitted-signal paths and two received-signal paths whoseinterleavers have an adjustable interleave depth.

Data packets coming from an arbitrary data source 5 are distributed by ademultiplexer 6 over the two latency paths LP or transmitted-signalpaths of the xDSL modem shown in FIG. 2. Conversely, the data receivedin the two received-signal paths are combined by a controlledmultiplexer 7 and are supplied to an arbitrary data processing unit 8.The demultiplexer 6 and the multiplexer 7 are actuated by a flowcontroller 1 via a control line 9. The flow controller 1 selects one ofthe two latency paths of the dual latency xDSL modem 2. The flowcontroller 1 preferably has a configuration memory 10 connected to it onwhich various configuration parameters prescribed by the networkoperator are set. The flow controller 1 based on the invention uses astandard control interface comprising a plurality of control lines toactuate the dual latency xDSL modem 2.

The xDSL modem 2 shown in FIG. 1 is on a linecard or subscriber linedriver card or in what is known as a DSLAM (Digital Subscriber LineAccess Multiplexer), for example. The xDSL modem 2 is formed by anintegrated semiconductor circuit, for example, and has interfaces basedon various standards.

The flow controller 1 is connected to various independent detectors. Avoice data detector 11 detects whether the data packets coming from thedata source 5 contain voice data. A video data detector 12 detectswhether the data packets coming from the data source 5 contain imagedata. As soon as the voice data detector 11 identifies that the datapackets contain voice data it outputs an appropriate indicator signal(Event Voice) to the flow controller 1. When the video data detector 12identifies that the incoming data packets contain image data it likewiseoutputs an appropriate indicator signal (Event Video) to the flowcontroller 1.

The voice data detector 11 and the video data detector 12 evaluate theheader data or data packet management data from the incoming datapackets. In one preferred embodiment, the traffic type VOICE or thetraffic type VIDEO is identified by checking the TCP or UDP port numberfor the data service used in the respective network.

Besides the voice data detector 11 and the video data detector 12, theflow controller 1 is additionally connected to an impulse noise detector13 and to a connection quality detector 14.

The detector 13 for detecting pulsed noise detects impulse noise sourceswhich briefly subject the transmission medium to a noise signal andwhose level is significantly above the level of the useful signal andhence makes reception of the useful signal impossible for a short time.Such pulsed noise signals normally last no longer than 2 msec. Thesafety margin, normally present for a DSL line, between the fixed noiselevel and the signal level of typically 6 to 30 dB does not provideadequate protection against pulsed noise signals.

In one preferred embodiment, the pulsed noise signal is identifiedthrough continuous observation of the signal-to-noise ratio SNR at thereception end of the xDSL modem.

In one alternative embodiment, CRC errors which arise are detected.

In another alternative embodiment, a pulsed noise signal is detected byevaluating not only the number of CRC errors which arise but also, inaddition, the results of the Reed-Solomon decoder provided at thereception end, i.e. the number of successfully corrected and uncorrectedRS code words.

The connection quality detector 14 is used to detect the connectionquality of the DSL link. To this end, the signal-to-noise ratio SNR iscontinually monitored and an average signal-to-noise ratio SNR iscalculated, for example. If the calculated average is above a prescribedthreshold value, the connection quality is rated as adequate. If theaverage is below the prescribed value, on the other hand, the connectionquality detector 14 outputs an indicator signal which indicates a poorconnection to the flow controller 1.

In alternative embodiments of the connection quality detector 14,coefficients as summarized in RFC2662, Definitions of Managed Objectsfor the ADSL Lines, IETF, August 1999, for example, are used. By way ofexample, “adslAtucPerfEss” or “adslAtucPerfEss” is monitored todetermine whether the count has increased by more than 3, for example,within a time interval of preferably 60 sec. If this is the case, theconnection quality detector 14 outputs an indicator signal Event LinkBad to the flow controller 1, indicating that the connection quality isinadequate.

The flow controller 1 takes the data traffic type detected using thedetectors 11, 12 as a basis for dynamically adjusting the datatransmission rate of the xDSL modem 2. To this end, the flow controller1 outputs control signals to an internal modem controller 2 a providedwithin the xDSL modem 2. The flow controller 1 controls the maximumtransmission rate of the two latency paths contained in the dual latencyxDSL modem (Max Link Rate LP0/1), a minimum transmission rate for thetwo latency paths LP0, LP1 (Min Link Rate 0/1), a maximum permissiblesignal delay via the two latency paths LP0/LP1 (Max Link Delay 0/1) anda minimum immunity toward pulsed noise signals for the two latency pathsMin Link INP0/1. In addition, the flow controller 1 outputs threecontrol signals SRA (Seamless Rate Adaptation), DRR (Dynamic RateRepartitioning) and SIC (Seamless Interleaver Change) to the internalmodem controller 2 a. The internal modem controller 2 a actuates theinternal latency paths LP within the xDSL modem 2.

In the case of SAR, there is a dynamic change in the number of bits perunit time which pass through a QAM modulator in the transmitted-signalpath of the xDSL modem, i.e. dynamic data rate adjustment takes place.This also entails settings being changed in a framer and in aReed-Solomon encoder connected downstream thereof.

In the case of DRR (Dynamic Rate Repartitioning), a data rate isdynamically distributed between the two latency signal paths LP0/LP1within the xDSL modem. The total rate, i.e. the sum of the two datatransmission rates, remains unchanged in this case, and only thesplitting ratio is changed. In this case, the framer and theReed-Solomon encoder may also be set as appropriate.

In the case of SIC (Seamless Interleave Change), there is a dynamicalteration in the interleave depth of the interleaver INT provided inthe respective latency signal path LP. The international standards forADSL and VDSL support SRA, DRR and SIC to different extents in line withthe table below:

ITU-T Standard SRA DRR SIC G.992.1, 2 No No No G.922.3, 5 Yes Yes NoG.993.1 No No No G.993.2 Yes Yes Yes

In one preferred embodiment, the inventive flow controller 1distinguishes between three different traffic types, namely a Datatraffic type VT_Data for web browsing, e-mails, FTP etc., a Voicetraffic type VT_Voice for Voice over IP applications and a Video traffictype VT_Video for image data applications.

For each traffic type, the network operator specifies configurationparameters a priori, particularly the maximum transmission rate for eachtraffic type, the minimum data transmission rate for each traffic typeand the maximum permissible delay time for the two traffic types Dataand Voice. Also, the permissible impulse noise duration for the traffictype Video is prescribed. The configuration parameters are stored in theconfiguration memory 10 shown in FIG. 1 and can be read by the flowcontroller 1.

Typical configuration parameter values are:

Data Voice Video MaxRate 24 Mbit/s 256 kbit/s 15 Mbit/s Min_Rate 128kbit/s 100 kbit/s 8 Mbit/s MaxDelay 8 ms 5 ms — MinINP — — 2 ms

Besides the configuration parameters which have been read, the flowcontroller 1 receives indicator signals or events from the detectors 11,12, 13, 14. The event EVTHINP indicates that pulsed noise has beenidentified by the impulse noise detector 13. The event Event Link Badindicates that connection quality detector 14 has identified adeterioration in the connection quality. The event Event Voice indicatesthat the voice data detector 11 has identified that the data trafficcontains voice data. The event EVT VIDEO indicates that the video datadetector 12 has identified that the data traffic contains video data.

In addition, the flow controller 1 receives connection parameters fromthe dual latency xDSL modem 2 via lines 15, namely the delay for the twolatency paths which has actually been caused by interleaving (Link DelayLP0/Link Delay LP1), the maximum repair time for protecting againstimpulse noise for the two latency paths (Link INP LP0, Link INP LP1),and the actual data rate for the two latency paths 0,1 (Link Rate LP0,Link Rate LP1).

As can be seen from FIG. 2, each transmitted-signal path or latency pathhas a framer for grouping the data into an xDSL frame and also anassociated error protection unit. The error protection unit comprises,in particular, a CRC encoder for generating a test digit, a scramblerfor scrambling the data which are to be transmitted, including thegenerated test digit, and also a Reed-Solomon encoder RS. The errorprotection unit has a respective interleaver INT connected downstream ofit which interleaves the encoded data. The interleave depth of theinterleavers can in this case preferably be set differently for thedifferent latency paths LP. Interleaving the information or distributingit in the course of time results in additional protection against noisesignals. However, interleaving results in an additional signalpropagation time. Typically, “Interleaving Delay” values of between 8and 20 msec. are required in order to achieve adequate protectionagainst impulse noise. The interleaved data are then associated withvarious carrier frequencies and are modulated by a QAM modulator. Next,inverse Fourier transformation, digital-analog conversion and pulseshaping using filters are carried out. Between the transmission andreception directions there is a hybrid circuit with echo cancellationEC.

The detectors 11, 12, 13, 14 are used for continuously observing thedata traffic for the occurrence of voice data, video data and formonitoring the physical connection for impulse noise and the generalquality of the connection. On the basis of the results of theseobservations, the flow controller 1 performs dynamic adjustment of thedata rate and also of the connection parameters relating to theprotection against impulse noise. The classified data traffic isallocated transmission paths within the modem, which meets thepreviously specified requirements of the data traffic. As a result ofthe dynamic adjustment of the connection parameters, i.e. withoutclearing down or setting up a connection again, the flow controller 1ensures a continually optimum connection quality for the various traffictypes. In this case, only the currently required part of the powerspectrum is used within a cable bundle, which means that the totalthroughput in the cable bundle is maximized.

FIG. 3 shows a flowchart of a preferred embodiment of the inventivemethod.

After a start step S0, the flow controller 1 is first of all used toinitialize the xDSL modem 2 in a step S1. In this case, the datatransmission rate of the xDSL modem 2 is initialized to a prescribedminimum transmission rate for transmitting data of the data traffictype. Following the initialization step S1, a counter or a timer T1 isstarted in step S2.

In a step S3, a check is first of all performed to determine whether ornot the incoming data packets contain voice data. If this is the casethen a subroutine A, as shown in FIG. 4, is executed in step S4.

If the incoming data packets do not contain voice data, the process iscontinued directly with step S5, i.e. the flow controller 1 checkswhether the video data detector 12 has identified the presence of imagedata. If the incoming data packets contain image data then thesubroutine B, shown in FIG. 5, is executed in step S6.

In step S7, the flow controller checks whether the connection qualitystipulated by the detector 14 is adequate. If the connection quality isnot adequate, the counter T1 is reset in step S8 and a subroutine C,shown in FIG. 6, is executed in step S9.

In step S10, the flow controller 1 checks whether the impulse noisedetector 13 is reporting impulse noise. If impulse noise is present thenthe counter is reset and started in step S11. Next, a subroutine D, asshown in FIG. 7, is executed in step S12.

In step S13, the flow controller 1 checks whether or not the counter T1has expired. If the counter has expired then the data rate of the xDSLmodem 2 is increased by means of SRA in step S14. Next, the counter T1is reset again and is restarted in step S15. The process then returns tostep S3.

In the inventive method, as shown in FIG. 3, the data transmission rateof the xDSL modem 2 is first of all set to a prescribed minimumtransmission rate for transmitting the “Data” traffic type in theinitialization step S1. As soon as the DSL connection has been set upand hence the fundamental capability of the xDSL modem to transmit thesum of all minimum required data rates is assured, the flow controller 1to this end reduces the data rate on the DSL line using the SRAmechanism by the minimum rates for the two traffic types “Voice” and“Video”, so that only the minimum required data transmission rate forthe “Data” traffic type is left. The additionally required datatransmission rates for voice and video are provided dynamically via theflow controller 1 only upon the actual occurrence of voice and videodata traffic. The data transmission rate or the bandwidth for the “Data”traffic type is provided permanently by the flow controller 1. The flowcontroller 1 first of all ensures that the transmission channel meetsthe minimum requirements by training the DSL connection with the sum ofthe minimum data transmission rate for all traffic types. So thatunnecessary signal spectra are not used up, the flow controller 1 thenreduces the data transmission rate to the minimum data transmission ratefor the “Data” traffic type in initialization step S1.

The flow controller 1 then uses the voice data detector 11 and the videodata detector 12 to monitor whether data of at least one further traffictype are transmitted. The data transmission rate of the xDSL modem 2 isset to a prescribed minimum total data rate for transmitting data of thedata traffic type and data of the other detected traffic type if othertraffic types, for example voice or video data, are detected by means ofthe detectors 11, 12. This dynamic adjustment of the data transmissionrates as required, i.e. when another traffic type arises, is effected bymeans of the subroutines A, B in steps S4, S6.

If, in step S7, the connection quality detector 14 identifies that theline conditions have deteriorated then the flow controller 1 checkswhether a higher data rate is set than is required as a minimum. To thisend, the flow controller 1 checks whether the data transmission rate ishigher than the sum of the minimum required data transmission rates ofall active traffic types. If this is the case then the data transmissionrate of the xDSL modem is reduced in steps by the flow controller 1using SRA. If it is not possible to reduce the data transmission rate,the physical limits have been reached and the xDSL modem 2 automaticallyclears down the xDSL connection completely on account of the bit errorswhich are beginning. The reduction in the data transmission rate for thecase of poor connection quality is the opposite of step S14, in whichthe data transmission rate is increased at regular intervals of time. Soto speak, the data transmission rate “breathes” with the prevailingconnection quality.

If the detector 13 for impulse noise reports to the flow controller 1the occurrence of impulse noise and if, at the same time, the “Video”traffic type is active, i.e. if guaranteed protection against impulsenoise sources is required, then the flow controller 1 first of allattempts to increase the signal propagation time to the highestpermitted value using SIC. If this is not possible, for example becausethe signal propagation time has already reached the maximum permissiblevalue, then the data transmission rate is reduced to the minimumrequired value. If this is not possible either then the flow controller1 uses the SRA mechanism to increase the gross data rate on thesubscriber line and to use the data rate gain in this case to addfurther forward error correction data. In this case, the flow controller1 makes use of the fact that longer signal propagation times result inlonger “smearing” of the data through interleaving and hence also ingreater protection against noise impulses. Accordingly, lowering thedata rate by increasing the signal-to-noise ratio SNR means a greaterprobability that noise impulses will not exceed their safety margin. Inthe case of the forward error correction, K data bytes are alwayscombined with R check bytes. In all DSL systems, the sum comprising theK data byte and the R check bytes is less than or equal to 255. When Ris large and k is small, protection against impulse noise can beimproved by reducing the number K of data bytes and increasing thenumber R of check bytes.

Using the timer or counter mechanism T1, the flow controller 1 based onthe invention sets the data transmission rate of the xDSL modem 2 to ahigher data transmission rate in steps. If a plurality of datatransmission systems are operating simultaneously which share a cablebundle containing a large number of subscriber lines 3, the distributionof the total bundle capacity is fairer than when the respective modemsare always set just to a fixed data transmission rate.

The inventive flow controller 1 initially sets the data transmissionrate to the minimum transmission rate for transmitting the “Data”traffic type. If none of the events which are checked by means of stepsS3, S5, S7, S10 occurs, the data transmission rate is increased in stepsat regular intervals of time in step S14. As a result, the availabletransmission channel is used only to the extent that is currentlyneeded, so that the crosstalk occurring on the adjacent datatransmission channels is as low as possible. This optimizes the overalluse of the channel bundle.

Following the initialization step S1, the flow controller 1 starts topoll the individual detectors 11, 12, 13, 14 continuously. If the voicedata detector 11 is used to detect the occurrence of voice data packets(Voice Over IP) then the flow controller 1 provides additional bandwidthfor voice data using SRA in step S4.

If the video data detector 12 identifies the occurrence of video datapackets then the flow controller 1 first of all checks whether there issufficient bandwidth available, so that the minimum required datatransmission rates are provided for all active traffic types. If this isthe case then the flow controller 1 takes no further measures. If thereis not sufficient bandwidth available then the flow controller 1requests the missing data transmission rate from the xDSL modem 2 usingthe SRA mechanism.

Various steps in the inventive method shown in FIG. 3 are described indetail below.

In step S1, the xDSL modem 2 is initialized by the flow controller 1.This involves the initialization being effected on the basis of whetherthe xDSL modem 2 is a dual latency xDSL modem having two latency signalpaths LP0, LP1 or an xDSL modem having just one latency path LP0.

If the xDSL modem is a modem having just one latency path LP then thedata transmission rate is chosen such that:LNK_RATE_(—) LP0=MinRate_(—) VT_Data+MinRate_(—) VT_Voice+MinRate_(—)VT_Video.  (1)

In addition, the maximum interleaving delay is set by the flowcontroller as follows:LNK_DELAY_(—) LP0<=Min(MaxDelay_(—) VT_Data,MaxDelay_(—) VT_Voice).  (2)

In this context, the shortest possible signal delay is chosen whichstill meets the requirement.

In addition, the flow controller 1 sets the framing parameter asfollows:MIN_(—) LNK _(—) INP _(—) LP0>=MinINP _(—) VT_Video.  (3)

If there is a conflict between the two above requirements (2), (3) thenthe flow controller 1 proceeds such that for the maximum interleavingdelay:LNK_DELAY_(—) LP0<=MaxDelay_(—) VT_Data  (4)with the smallest possible delay being chosen for which the requirementis still met.

In addition, the framing parameter is set such that:LNK _(—) INP _(—) LP0>=MinInp _(—) VT_Video  (5)

If requirements (2) and (3) are in conflict with one another then theflow controller 1 first of all ignores the signal delay requirement forvoice data, assuming that the interleaving delay is dynamically reducedfor later phases with voice communication.

In addition, the data paths are connected by the flow controller 1 suchthat all three traffic types are put onto the latency path LP0.

Following successful connection setup, the data transmission rate forthe latency path LP0 is reduced by (MinRate_VT_Voice+MinRate_VT_Video)by the flow controller using SRA.

This concludes the initialization in step S1 of the xDSL modem 2.

If the xDSL modem 2 has two separate latency paths LP0, LP1, theinitialization in step S1 by the flow controller 1 takes place asfollows.

If MaxDelay_VT_Data<=MaxDelay_VT_Voice, the data transmission rate forthe latency path LP0 is chosen such that:LNK_RATE_(—) LP0=MinRate_(—) VT_Data+MinRate_(—) VT_Voice.  (6)

Next, the maximum interleaving delay by the latency path LP0 is set bythe flow controller 1 such that:LNK_DELAY_(—) LP0<=MaxDelay_(—) VT_Data.  (7)

The data transmission rate for the latency path LP1 is then set by theflow controller 1 such thatLNK_RATE_(—) LP1=MinRate_(—) VT_Video.  (8)

The flow controller 1 then sets the framing parameter for the latencypath LP1 such that:LNK _(—) INP _(—) LP1>=MinINP _(—) VT_Video.  (9)

The data paths are then connected such that the “Voice” traffic typeVT_Voice and the “Data” traffic type VT_Data are transmitted on thesignal path LP0.

In addition, the data paths are connected by the flow controller 1 suchthat the “Image Data” traffic type VT_Video is put onto the latency pathLP1 of the dual latency modem 2.

Immediately after successful connection setup by the xDSL modem, thedata transmission rate for the latency path LP0 LNK_Rate_LP0 is reducedby MinRate_VT_Voice by the flow controller 1 using SRA/DRR. Thetransmission rate for the latency path LP1 LNK_Rate_LP1 is reduced byMinRate_VT_Video by the flow controller 1 using SRA/DRR.

If MaxDelay_VT_Data>MaxDelay_VT_Voice then the latency path LP0 is usedfor voice and the latency path LP1 is used for video and data.

The flow controller then sets the data rate for the latency path LP0such that:LNK_RATE_(—) LP0=MinRate_(—) VT_Voice.  (10)

The maximum interleaving delay for the latency path LP0 is then set suchthat:LNK_DELAY_(—) LP0<=MaxDelay_(—) VT_Voice.  (11)

Next, the data rate for the latency path LP1 is set by the flowcontroller 1 such that:LNK_RATE_(—) LP1=MinRate_(—) VT_Video+MinRate_(—) VT_Data.  (12)

Next, the maximum interleaving delay for LP1 is set by the flowcontroller 1 such that:LNK_DELAY_(—) LP1=MaxDelay_(—) VT_Data.  (13)

The framing parameters are set by the flow controller 1 for the latencypath LP1 such that:LNK _(—) INP _(—) LP1>=MinINP _(—) VT_Video.  (14)

Finally, the data paths are connected by the flow controller 1 such thatthe traffic type VT_Voice is put onto the latency path LP0 and thetraffic types VT_Data and VT_Video are put onto the latency path LP1.

Immediately after successful connection setup, the data transmissionrate for the latency path LP0 (LNK_RATE_LP0) is reduced byMinRate_VT_Voice by the flow controller 1 using SRA/DRR. The datatransmission rate for the latency path LP1 (LNK_RATE_LP1) is reduced byMinRate_VT_Video by the flow controller 1 using SRA/DRR.

This concludes the initialization of the dual latency xDSL modem 2 instep S1.

When the counter T1 has started in step S2, the flow controller 1monitors various events using the detectors 11, 12, 13, 14 in steps S3,S5, S7, S10.

In step S14, the expiry of the counter T1 results in the data rate beingincreased in steps using SRA until the sum of the respective permissiblevalues for all active traffic types has been reached. When a poorconnection or a pulsed noise signal occurs, the counter T1 is reset,i.e. increasing the data rate is not continued if the line qualitydeteriorates. As a result, the xDSL modem 2 only ever outputs as muchpower to the subscriber line 3 as is required for the respective datatraffic situation. Hence, the capacity available in a cable bundlecontaining a large number of lines is utilized in optimum fashion. Theinventive flow controller 1 therefore carries out dynamic spectrummanagement.

If the xDSL modem 2 is a dual latency modem then during initializationby the flow controller 2 the “Voice” traffic type is combined with thatof the other two traffic types in a latency path LP, which has a lowerpropagation time requirement than voice. The comparison for the shorterpropagation time is preferably made only with the “Data” traffic type,since in practice video data always have a longer permissiblepropagation time than voice data. If there is not a lower propagationtime requirement than for the “Voice” traffic type for the data trafficthen a latency path LP is reserved exclusively for voice datatransmission, and the video and data traffic share the other latencypath.

In the case of a dual latency xDSL modem, the data rates are chosen bythe flow controller 1 for each latency path such that the sum of theminimum data transmission rates corresponds to the respective traffictypes provided. The maximum permissible propagation time is chosen suchthat the most stringent of all the propagation time requirements of therespectively provided traffic types is met. That latency path LP whichis transmitting video data is configured in line with the requirementfor minimum protection against impulse noise sources.

As soon as the connection has been set up and hence the fundamentalcapability of the xDSL modem 2 to transmit the sum of all minimumrequired data transmission rates is assured, the flow controller 1reduces the data transmission rate on the DSL line 3 using the SRAmechanism by the minimum rates for voice and video in the respectivelatency path LP, so that only the minimum required rate for data trafficis left. The DRR mechanism is then used to associate the entire datatransmission rate with that latency path which is transmitting datatraffic, while the other latency path is reduced to a data rate of 0.The additionally required data transmission rates for voice and videoare provided dynamically by the flow controller 1 only upon an actualoccurrence of voice or video traffic. By contrast, the bandwidth fordata is provided by the flow controller 1 permanently.

The inventive flow controller 1 is based on the following practicalrequirements, namely:

In principle, a sufficiently high data transmission rate needs to beprovided for simultaneous transmission of all three traffic types on therespective transmission channel.

The required, maximum data transmission rate of the “Data” traffic typeis much higher than the data transmission rate for the “Voice” traffictype.

The required maximum data transmission rate for the “Video” traffic typeis much higher than the data transmission rate for the “Voice” traffictype.

A transmission option for the “Data” traffic type is provided by theflow controller 1 permanently.

For the transmission of video and voice data, a minimum datatransmission rate must not be undershot.

For the transmission of voice data, a maximum propagation time must notbe exceeded.

For the transmission of video data, a minimum level of security againstimpulse noise is assured by the flow controller 1.

In this context, the observance of the minimum propagation time forvoice data is rated more importantly than the fulfillment of the minimumlevel of security against impulse noise in the case of video datatransmission.

The transmission system is set to either one or two data transmissionpaths or latency paths from the outset.

Video and voice data are not transmitted permanently, but rather onlywhen required.

The inventive flow controller 1 allows the data transmission rate forthe “Data” traffic type to fluctuate, since this is not a problem.

The inventive arrangement, as shown in FIG. 1, is preferably used at theexchange end, i.e. by the network operator. The data source 5 representsa packet-based transport network belonging to the network operator,including the gateway to the Internet.

The inventive method has been described by way of example with referenceto three traffic types, namely. “Data”, “Voice”, and “Video”. In analternative embodiment, data streams of these and other traffic typesare controlled.

What is claimed is:
 1. A method for transmitting data of various traffictypes utilizing an xDSL modem comprising: detecting the traffic types ofthe data which are to be transmitted, setting a data transmission rateby a flow controller, and dynamically adjusting a data transmission ratefor the xDSL modem based on the detected traffic types.
 2. The method ofclaim 1, further comprising: initializing a data transmission rate forthe xDSL modem to a prescribed minimum transmission rate fortransmitting data of a data traffic type; detecting whether data of atleast one other traffic type needs to be transmitted by the xDSL modem,and setting the data transmission rate to a prescribed minimum totaldata rate for transmitting data of the data traffic type and data of thefurther detected traffic types; increasing the set data transmissionrate in steps at prescribed intervals of time; and reducing the set datatransmission rate to the minimum total data rate if a deterioration inconnection quality is detected.
 3. The method of claim 2, wherein thevarious traffic types comprise a data traffic type for transmittingdata, a voice traffic type for transmitting voice data, and a videotraffic type for transmitting image data.
 4. The method of claim 1,wherein the flow controller sets the data rate using a data transmissionrate algorithm.
 5. The method of claim 4, wherein the data transmissionrate algorithm utilizes Seamless Rate Adaptation.
 6. The method of claim1, wherein a voice data detector connected to the flow controller isused to detect whether data packets coming from a data source comprisevoice data or image data.
 7. The method of claim 1, further comprisingdistributing the data to be transmitted over various transmitted-signalpaths for the xDSL modem by a time-division demultiplexer.
 8. The methodof claim 1, wherein a test digit for the data which are to betransmitted is generated by a CRC encoder.
 9. The method of claim 8,wherein the data to be transmitted, including the generated test digit,are scrambled by a scrambler.
 10. The method of claim 9, wherein thescrambled data are encoded by a Reed-Solomon encoder.
 11. The method ofclaim 10, wherein the data encoded by the Reed-Solomon encoder areinterleaved by an interleaver having an adjustable interleaver depth.12. An apparatus for transmitting data of various traffic typesutilizing an xDSL modem, comprising: at least one detector used todetect at least one traffic type of data which is to be transmitted,wherein the detected traffic type can be taken as a basis fordynamically adjusting a data transmission rate for the xDSL modem, and aflow controller, wherein the data transmission rate of the xDSL modemcan be set by the flow controller utilizing Seamless Rate Adaptation.13. The apparatus of claim 12, further comprising: a device forinitializing a data transmission rate for the xDSL modem to a prescribedminimum transmission rate for transmitting data of a data traffic type;a device for detecting whether data of at least one other traffic typeneeds to be transmitted by the xDSL modem, and for setting the datatransmission rate to a prescribed minimum total data rate fortransmitting data of the data traffic type and data of the furtherdetected traffic types; a device for increasing the set datatransmission rate in steps at prescribed intervals of time; and a devicefor reducing the set data transmission rate to the minimum total datarate if a deterioration in connection quality is detected.
 14. Theapparatus of claim 13, wherein the various traffic types comprise a datatraffic type for transmitting data, a voice traffic type fortransmitting voice data, and a video traffic type for transmitting imagedata.
 15. The apparatus of claim 12, wherein a voice data detectorconnected to the flow controller can be used to detect whether datapackets coming from a data source contain voice data.
 16. The apparatusof claim 12, wherein a video data detector connected to the flowcontroller can be used to detect whether data packets coming from a datasource comprise image data.
 17. The apparatus of claim 12, wherein thedata to be transmitted can be distributed over varioustransmitted-signal paths for the xDSL modem by a time-divisiondemultiplexer.
 18. The apparatus of claim 17, wherein the distributeddata in each transmitted-signal path can be grouped by a framer to forma frame.
 19. The apparatus of claim 18, wherein the data to betransmitted which are grouped in a frame on each transmitted-signal pathcan be encoded by an associated error protection device in order toprotect against transmission noise.